It is important to maintain a deep draft vessel over the center of a narrow channel to prevent the vessel from going aground, which occurs when the hull of the vessel actually strikes and becomes imbedded in the wall of the channel. Navigation of a channel is typically made by observing center channel markers, or buoys, which are positioned to identify the approximate location of the edge of the channel and thereby define a pathway for floating vessels over channel center. Guiding a vessel over the center of a channel is sometimes difficult, however, because the channel markers are widely spaced and obscurred by poor visibility. Thus, unless the navigator has had prior experience in the channel, there is a good likelihood that his course will depart from the center of the channel.
In practice, the navigator will generally rely on his depth monitor to assure that the depth of the channel is always greater than the draft of the vessel. Conventional depth monitors, however, only determine depth at one point. A single point depth reading does not inform the navigator where the vessel is located within the channel. Even though the depth reading on a conventional depth monitor will show that the vessel is venturing into shallow water at a channel, the navigator frequently is unsure on which side of the center of the channel the vessel is located, and he therefore does not know which way to steer the vessel to find channel center.
A need therefore exists for instrumentation that identifies the position of a vessel within a channel and indicates to a navigator a steering position for guiding the vessel to and maintaining the vessel above the center or deepest part of the channel. Because steering direction often must be determined almost instantaneously to avoid going aground, a need further exists for instrumentation that displays a single steering direction command, i.e., port, starboard or maintain course, to the navigator or generates an automatic rudder control, to maintain the vessel in channel center.
Accordingly, one object of the invention is to provide a method of and apparatus for indicating the position of a vessel within a channel.
Another object is to provide a method of and apparatus for automatically determining the position of a vessel within a channel and displaying steering commands for guiding the vessel with respect to the channel center.
Another object is to provide a method of and apparatus for automatically determining the location of the center or deepest part of a channel with respect to a vessel and for generating steering command signals for guiding the vessel over the channel center.
Another object is to provide a method of and apparatus for determining the center or deepest part of the channel with respect to the vessel and for generating steering control signals for automatically guiding the vessel over the channel center.
Another object is to provide a method of and apparatus for channel navigation usable in unmarked channels and providing unambiguous display of steering directions to the navigator so that course correction can be undertaken immediately.
In U.S. Pat. No. 3,267,417 to Galloway, a navigation system for maintaining a vessel over channel center comprises a series of transponders located on the floor of the deepest part of the channel, a pulse transmitter located at the bow of the vessel and directed toward the transponders and a pair of hydrophones mounted athwartship and equally distant from the center line of the vessel. The transmitter transmits beams that are reflected from the channel transponders and received by the hydrophones to generate steering signals for maintaining the vessel in channel center. The Galloway system, however, requires that the channel be marked with transponders for the purpose of reflecting beams generated by the vessel-carried transmitter. The system is not usable for navigation in unmarked channels.
Another object of the invention, therefore, is to provide a channel navigation system that requires no external channel marking.
Another object is to provide a center channel navigation system that is usable with respect to unmarked channels and requires no apparatus external to the vessel.